This invention relates to an illumination system for illuminating a display device, comprising a light-emitting panel and a light source for coupling light into the light-emitting panel, said light source including a low-pressure mercury-vapor discharge lamp.
The invention also relates to a display device comprising said illumination system.
Such illumination systems are known per se and are also referred to as edge lighting systems. They are applied, inter alia, as back lighting for (image) display devices, for example for television receivers and monitors. Such illumination systems can particularly suitably be used as back lighting for non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are employed in (portable) computers or (cordless) telephones.
Said display devices generally comprise a substrate provided with a regular pattern of picture elements (pixels), which are each controlled by at least one electrode. In order to reproduce an image or a datagraphic display in a relevant area of a (display) screen of the (image) display device, the display device employs a control circuit. In a LCD device, the light originating from the backlight is modulated by means of a switch or a modulator, and various types of liquid crystal effects are employed. In addition, the display may be based on electrophoretic or electromechanical effects.
In the illumination systems mentioned in the opening paragraph, a tubular low-pressure mercury-vapor discharge lamp, for example one or more cold cathode fluorescent lamps (CCFL), is used as the light source, the light emitted, in operation, by the light source being coupled into the light-emitting panel which serves as an optical waveguide. This optical waveguide generally forms a comparatively thin, flat panel which is made of, for example, a synthetic resin or glass, with light being transported through the optical waveguide under the influence of (total) internal reflection.
An illumination system of the type mentioned in the opening paragraph is disclosed in EP 749 550. In said document, a description is given of a flat light source provided with a low-pressure mercury-vapor discharge lamp for illuminating a LCD device comprising a light-emitting panel having a light-emission window, which panel is provided with a light input edge surface for coupling light into the light-emitting panel, and the illumination system comprises a light-mixing chamber whose longitudinal direction is parallel to said light input edge surface and provided with a low-pressure mercury-vapor discharge lamp, said light-mixing chamber being associated with the light input edge surface.
A drawback of the known illumination system is that the light source has a fixed electromagnetic spectrum.